1. Field of the Invention
The present invention relates to optical detection devices and more particularly to a novel optical detection device for use in examining paper currency for genuineness during a high speed handling and counting operation.
This invention relates to a detector of counterfeit currency as contrasted to genuine U.S. paper currency of any denomination.
The present invention is directed to a counterfeit currency detector so as to provide a quick and simple means for detecting counterfeit U.S. paper currency. The invention requires little or no skill to use. The invention may be used to validate paper currency of any origin or country.
2. Description of the Prior Art
The present invention relates to the examination of bills or other currency for purposes such as determining their authenticity and denomination, and more particularly to methods and apparatus for achieving a high level of acceptance of valid bills or currency while simultaneously maintaining a high level of rejection of non-valid bills or currency, such as counterfeits. While the present invention is applicable to testing of bills and other currency, for the sake of simplicity, the exemplary discussion which follows is primarily in terms of paper currency.
The application of the present invention to the testing of paper money, banknotes and other currency will be immediately apparent to one of ordinary skill in the art.
It has long been recognized in the field of bill and currency testing that a balance must be struck between the conflicting goals of "acceptance" and "rejection"--perfect acceptance being the ability to correctly identify and accept all genuine items no matter their condition, and perfect rejection being the ability to correctly discriminate and reject all non-genuine items. When testing under ideal conditions, no difficulty arises when trying to separate ideal or perfect bills from bills or counterfeit bills that have different characteristics even if those differences are relatively slight. Data identifying the characteristics of the ideal bills can be stored and compared with data measured from a bill or bill to be tested. By narrowly defining bill acceptance criteria, valid bills that produce data falling within these criteria can be accepted and bills that produce data falling outside these criteria can be rejected. A well-known method for bill acceptance and bill rejection is the use of bill acceptance windows to define criteria for the bill acceptance. Of course, in reality, neither the test conditions nor the bills to be tested are ideal. Windows or other tests must be set up to accept a range of characteristic bill data for worn or damaged genuine bills, and also to compensate for environmental conditions such as extreme heat, extreme cold, humidity and the like. As the acceptance windows or other bill testing criteria are widened or loosened, it becomes more and more likely that a bill or counterfeit bill will be mistakenly accepted as genuine. As test criteria are narrowed or tightened, it becomes more likely that a genuine bill will be rejected.
Genuine U.S. currency has a magnetic property which is capable of being detected by a magnetic sensor. A hysteresis curve in which magnetization is plotted against magnetizing force of the black ink on a U.S. one dollar bill. The plot is in units of EMU and Oersteds. The plot of the retentivity of black ink on U.S. paper currency is significantly less than the saturation level, indicating that it is preferable to sense the saturation level rather than the retentivity level. This can be accomplished by magnetizing the bill at the sensing location. Previous attempts to accomplish this suffer from the following problems:
1. The magnet tends to saturate the mu-metal shield surrounding the magnetic pick up head, thereby reducing the shielding effectiveness, and PA1 2. The magnet tends to vibrate during machine operation causing an unacceptable magnetic noise source.
In order to solve these problems, the present invention is characterized by comprising a optical head which is utilized as the optical scanning instrument thereby completely eliminating the need for a permanent magnet. In addition, the problems of reduced shielding effectiveness and unacceptable optical noise cannot arise.
The present invention relates to counterfeit detectors for United States paper currency. With modern improvements in copying methods it has become relatively easy for counterfeiters to reproduce paper currency. The production of passable copies no longer requires the work of a skilled engraver. Photographic methods can be used to make accurate plates in a very short time. In addition electrostatic copying equipment has been so perfected that reasonable color copies of legitimate notes can be made easily and rapidly. As a result there has been a steadily growing amount of false currency and an increased cost to merchants and others who must absorb the loss when these copies are passed.
Some methods to detect counterfeit employ special illumination. Because United States bills are printed on rag bond and use no brighteners, they possess characteristic optical properties. Under ordinary light they will have an off-white appearance. Under ultraviolet illumination they will not fluoresce. Papers containing wood pulp and brighteners will not have these properties. A new paper has become available to some counterfeiters however which more closely resembles that used for legitimate notes.
Despite the use of previous optical machines the most effective detection of counterfeit to date has been by highly trained observers who look for small imperfections in the printing.
Prior to the present invention there have existed devices for the detection of counterfeit currency, which devices range in degree of complexity, all of which are requisite of many complicated parts and normally require an operator with considerable skill in order to make proper determinations of the fact of counterfeit currency. Included within the prior art detectors are those which utilize at least partially ultra-violet radiation together with necessary complicating elements.
It has been ascertained through tests and investigations that almost all genuine paper currency made by the U.S. Mint is made from paper which does not include any fluorescent dyes, optical bleaches, or pigments. When genuine paper currency is illuminated by ultraviolet light from approximately 2,500 to approximately 4,000 angstrom units, the currency generally does not exhibit a chromamorphic response other than that naturally attributable to the cotton or linen stock. In recent years, even the U.S. Mint has had difficulty in obtaining rag stock completely free from fibers containing optical bleaches or other fluorescent materials.
Almost all counterfeit currency printed in the past 15 years has been made from rag stock which has a definite chromamorphic response in the blue range when activated by properly filtered ultraviolet light. The present invention does not respond to this descrepency independent of the search of the plate numbers and the invention is predicated thereon.
Occasionally, genuine U.S. paper currency contains isolated fibers which exhibit a chromamorphic response. This is particularly, but not exclusively, true with respect to 10 and 20 dollar bills from the 1963 series. The response exhibited by such currency can be distinguished, with some experience, from counterfeit currency in which the entire unprinted paper surface exhibits a uniform, unbroken fluorescence in blue range, varying in brightness with the amount of optical bleach in the paper stock.
Much counterfeit paper currency, although containing optical bleach, may have a low level of chromamorphic response which is indistinguishable, or nearly so, from legal paper currency, when viewed in an area of high ambient visible light. Besides the fact that on occasion genuine paper currency will exhibit a chromamorphic response which might confuse someone other than a viewer who is well trained or instructed, there are other explanations for possible confusion. For example, genuine currency is often left in wearing apparel which is washed in a bath containing a high amount of optical bleach. Some of the bleach is absorbed by the paper stock and tends to lead one to suspect it as being counterfeit. After viewing tens of thousands of bills in banks, only two such bills have come to our attention. Hence, after considerable experimentation, it has been ascertained that there is another characteristic of genuine paper currency which will facilitate further tests in confirmation of counterfeit currency. It has been ascertained that the black ink used to print the intaglio impression of genuine paper currency has optical characteristics which are detectable and will exhibit the specific reaction to a optical field. It is believed that the incorporation of optical pigment in the black ink has been a specification for genuine paper currency since 1941. The present invention contemplates subjecting any suspected counterfeits to a optical field and the lack of any response will be confirmation that the particular paper currency is counterfeit.
One example of the use of such windows is described in U.S. Pat. Nos. 3,918,564 and 3,918,565, both assigned to the assignee of the present invention. U.K. Application Serial. No. 89/23456.1 filed Oct. 18, 1989, and assigned to the assignee of the present invention, is one response to the real world compromise between achieving adequately high levels of acceptance and rejection at the same time. This U.K. application describes techniques for establishing non-uniform windows that maintain a high level of acceptance while achieving a high level of rejection.
Another prior art approach is found in the Mars Electronics IntelliTrac..TM.. Series products. The IntelliTrac..TM.. Series products operate substantially as described in European Patent Application EP 0 155 126, which is assigned to the assignee of the present invention.
Examples of such prior detectors are disclosed in U.S. Pat. No. 2,951,164, and U.S. Pat. No. 2,950,799 both of Timms, and U.S. Pat. No. 3,618,765 to Cooper. With regard to the latter, there is disclosed a viewing window having ultra-violet light bulbs mounted immediately therebeneath with bulbs and the viewing window being above a flat mounting surface available through a port for the insertion of currency to be examined. This particular Cooper apparatus requires that the reflected ultra-violet light be viewed through a window having a filter therein, the filter of necessity having a light blue color thereby permitting the viewing of the light blue or bluish-white chromamorphic response of counterfeit paper currency under the ultra-violet light from the ultra-violet bulbs.